Green State Joining Of ZrO₂ To Al₂O₃ Ceramics With Polymer/layered Silicate Nanocomposites And Study Of The Joining Mechanism

Joining of advanced ceramics has become a dynamic field of development since it provides possibilities of manufacturing of complex-shaped components, which are not possible or not cost-effective by existing techniques of green state shaping and/or machining. Although there has been some successful experiments in green state joining of ceramics, there were limited in the area of joining ceramics with similar properties such as thermal expansion coefficients, sintering shrinkage et al. Therefore, joining dissimilar, oxide ceramics with different properties is truly challenging but necessary. Zirconia and Alumina is commonly used in many fields because of their good properties. The problem is that ZrO2 and Al2O3 have great difference in physical properties such as thermal expansion coefficients, sintering shrinkage, density, particle size et al. which made the joining of ZrO2 and Al2O3 relatively difficult. In this paper, a new method of joining Al2O3 to ZrO2(8YSZ) ceramics on green state, using a polymer/layered silicate (PLS) nanocomposites-containing slurry, without applied pressure, is reported. ZrO2 (8YSZ) and 95Al2O3 ceramics were successfully joined in green state and a maximum bond strength is reached when the PLS adhesive contents in the interlayer is 3⁵wt%. The PLS adhesive takes an important role in joining. The joint strength reduced with the increasing of the interlayer thickness. Effect of sintering temperature and holding time on the bond strength of the joints was investigated. A maximum strength is obtained as sintering temperature is 1550℃ and hold time is 120mins. SEM microstructure analysis of interfaces between Al₂O₃ and ZrO₂ showed that the particles in both interfaces closely inlayed and integrated each other with less deformation, cracks and pores, although grains within the joint and within the joined couples clearly differ in size and morphology. The grain size of the particles grown in the joint was smaller than that in the matrix ceramics The joining mechanism was determined to be the diffusion reaction at the interface and the interlocking of particles in the joining zone as the temperature increased. This technique is suitable for joining of various kinds of advanced ceramics.